@MaxBooBooBear:
My female german shepherd mix was spayed at a young age, and I never saw any breeding urges from her. But I never saw any breeding urges from Max, my male B who was neutered at 6 months either. The only thing Max did was chatter his little jaws if a female in heat had been around and left any scent..
Hee hee! So "breeding" urge signals were or are present with your neutered male, Max - seemingly by the jaw chattering. However with females, the question is if they experience something - with Daisy having determination to over-alpha Duke. I know, it's a strange phenomenon, but something's happening to the status quo between them - excessive squabbling, etc. It's possible, Daisy is in her "fed up with you, Duke" cycle of life.